1. Field
Embodiments of the present invention generally relate to a tubular lamp. More particularly, embodiments described herein relate to a tubular lamp for a rapid thermal processing (RTP) apparatus.
2. Description of the Related Art
RTP systems are employed in semiconductor chip fabrication to create, chemically alter, or etch surface structures on semiconductor substrates or wafers. RTP typically depends upon an array of high-intensity incandescent lamps fit into a lamphead and directed at the substrate. The lamps are electrically powered and can be very quickly turned off and on and a substantial fraction of their radiation can be directed to the substrate. As a result, the substrate can be very quickly heated without substantially heating the chamber and can be nearly as quickly cooled once the power is removed from the lamps.
Typically the lamps for RTP apparatus are single-ended lamps each having a socket for electrical contact disposed at one end of the lamp. The single-ended lamps generally are oriented vertically with respect to the substrate. In this configuration, only the end opposite the socket is directed at the substrate, while the elongated body of the lamp radiates heat in a direction that is parallel to the substrate. Typically, about half of the radiant energy from the lamp goes out towards the substrate. About half of the radiant energy from the lamp is absorbed in the lamp and in the lamphead structure. This can cause the lamp to reach much higher temperatures as compared to a lamp radiating in open space. If the lamp gets too hot, the average lamp lifetime can be substantially reduced. Heat absorbed in the lamphead can also cause the lamphead to deform. One approach to maintain the same radiation energy output while reducing the filament temperature is to increase the surface area of the filament inside the single-ended lamp, such as providing an overwind to the filament. However, it is desired to have a higher heating efficiency and lower filament temperature.
Therefore, there is a need for an improved lamp for a RTP apparatus.